Dynamic performance of an organic Rankine cycle system with a dynamic turbine model: A comparison study

Abstract

Particular interest has been shown in the dynamic modeling and the operation of organic Rankine cycle (ORC) systems, which have emerged to harvest energy from low-grade heat sources. In conventional studies corresponding to ORC dynamics, the turbine is generally modeled as a steady-state component, and the efficiency, mass flow rate, and rotational speed of the turbine are less concerned, which may lead to inaccuracy of the system performance during dynamic operations. In this paper, the dynamic model of an ORC system is established, and a comprehensive dynamic turbine model is considered for the first time in such studies. The turbine 1D design and off-design is performed, and the mass inertia and the rotational inertia are also considered in the turbine model. In two operation modes, the dynamic responses of the ORC system to severe disturbance of the heat source parameters are investigated and compared with systems applying conventional steady-state models. Considerable differences have been shown in terms of turbine efficiency (with a maximum relative error of 12.9%), mass flow rate (with a maximum relative error of 8.3%), and net power output of the ORC systems using different turbine models. Furthermore, the use of the dynamic turbine model has extended the settling time and undershoot of the controlled parameter. This study reveals that the dynamic turbine model should be carefully considered in investigations related to ORC dynamics.